(a) Technical Field
The present invention relates to an electromechanical brake, more particularly, to an electromechanical brake capable of quickly releasing braking force and improving braking performance of a vehicle even when a power source breaks down.
(b) Description of the Related Art
In general, a brake device for a vehicle is a device that generates braking force for decelerating or stopping a moving vehicle or maintaining the vehicle in a stopped state, and the braking is carried out while kinetic energy of the vehicle is converted into thermal energy by mechanical friction when the vehicle decelerates, and frictional heat is radiated into the atmosphere.
As the brake device for a vehicle, there are a drum type hydraulic brake, a disc type hydraulic brake, and the like, and the disc type hydraulic brake obtains braking force by strongly pressing friction pads against both surfaces of a disc, which rotates together with a wheel, instead of using a drum.
However, the hydraulic brake has a complicated structure because it requires mechanical elements connected to a brake pedal in front of a driver seat, hydraulic piping, elements for controlling hydraulic pressure, and the like, and therefore, an electromechanical brake (EMB) has been developed and used to simplify a configuration of the brake device.
Unlike the typical hydraulic brake, the electromechanical brake refers to a brake that obtains braking force by pressing a friction pad by using a mechanical mechanism driven by an electric motor.
The typical electromechanical brake has an actuator including the electric motor that rotates forward and backward in order to perform the braking operation (press the friction pad) and release the braking operation (reduce pressure), and the electromechanical brake operates to press the friction pad using rotational force of the motor so that the friction pad presses the disc (causes friction with the disc) at the time of performing the braking operation.
Compared to the hydraulic brake, the electromechanical brake has a simple structure and a high response speed, and may be more precisely controlled, thereby improving braking safety.
The electromechanical brake is advantageous because braking force is easily controlled, and essentially used to implement a brake-by-wire (BBW) system.
Meanwhile, the electromechanical brake generates braking force from electric power by using the motor and a mechanical transmission mechanism as described above, and in this case, most electromechanical brakes use a principle of screws such as bolts and nuts, and convert rotational force of the motor into translational force for pressing the friction pad.
In the related art, Korean Patent No. 10-1220405 (Jan. 3, 2013) discloses an electromechanical brake in which when rotational force of a motor is transmitted via a reduction gear to an operating shaft thread-coupled to a piston, the rotational force is converted into translational force by a screw structure between the piston and the operating shaft.
In the electromechanical brake, clamping force is generated by a pressing operation of the piston, and the brake disc is pressed by the clamping force, such that braking force is generated.
However, in a case in which a power source, which supplies electric power for operating to the motor, breaks down in the electromechanical brake in the related art, braking force may not be sufficiently released after the braking force is generated, because of motor cogging torque, internal friction, or the like.
That is, torque, which allows the motor to rotate in a reverse direction, is generated due to a clamping force of a caliper housing when the power source breaks down at the time of performing the braking operation, but the torque in the reverse direction is cancelled out due to motor cogging torque, friction between gears in a decelerator, friction of the operating shaft, friction of the piston, and the like, and as a result, the braking force may not be sufficiently released. Therefore, while the vehicle is moving, differential braking may occur, and as a result, a dangerous situation such as spinning of the vehicle may be caused.
Therefore, there is a need for a technology that may prevent a wheel from being locked and quickly release braking force such that motion stability of the vehicle does not deteriorate when a power source for powering the electromechanical brake breaks down.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.